It is proposed to investigate the mechanisms which govern proliferation of capillary blood vessels in the microvascular system during pathological processes such as wound healing. Studies will focus on the role of endothelial cells in determining: the structure of the new capillaries, their mode of growth through connective tissue and their eventual regression or remodelling to form arteries and veins. Regressing vessels will be studied mainly in animals where vessel growth can be quantitated and observed in vivo, although some tissue culture experimentation will be performed. Electron microscopic, histochemical and autoradiographic studies will be supported by some biochemical studies to investigate the ability of endothelial cells to synthesize extracellular macromolecules or alter the synthetic activity of connective tissue cells during capillary growth. In addition, the structural changes which occur in remodelling capillaries will be correlated with their functional capacity. The events responsible for initiating capillary regression will be investigated. Whenever possible, regenerating vessels in adult animals will be compared to developing blood vessels in embryonic systems in order to investigate common mechanisms which animals use to achieve and control capillary growth.